Visit the Chicago Botanical Gardens, and have fun taking LOTS of pictures!
See what Broadway Shows are playing. It's one of my favorite things to do.
Visit the Art Institute and the Museum of Science and Industry.
Visit the "Museum Campus" (Shedd Aquarium, Adler Planetarium, and Field Museum all located here) and have the opportunity to get your picture taken with the beautiful Chicago skyline in the back.
Go on the Chicago Architectural Boat Tour. Lots of history and great photography opportunities.
Even just strolling through the "loop" in Chicago, will give you some great photo opportunities.
Unless it's really important to you, I'd skip Navy Pier. You aren't bringing your children and many of the activities there are geared toward families.
There are a couple of food tours in Chicago. I suggest you look on TripAdvisor (.com) and get a better idea of what you'd like to do in Chicago.
As far as foodies, go to Ann Sather's and have their cinnamon rolls.

They were featured on Food Network as one of the "Best Things I Ever Ate". Although it's a chain, I also recommend Ruth's Chris. It seriously is the best steak I ever had. However, may I also suggest the Signature Room (at the top of the John Hancock building) for a "signature" Chicago experience. For something out of the ordinary and definitely romantic I suggest Geja's Cafe in Lincoln Park. It's a fondue restaurant. It was also featured on Food Network as one of the most romantic places to dine. The food is delicious. Lincoln Park is also a really neat neighborhood with lots of unique shops and places to dine. Oh, be sure to find a place to get a Chicago style hot dog and stop at Garrett's for some popcorn. Even better, grab a hot dog and some popcorn and have a picnic at Millenium Park. Here you can people watch and see the amazing structures (and get the standard picture with the "Bean").